Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Table 15-2
DMP parameters that are tunable (continued)
DescriptionParameter
The time for which an intermittently failing path
needs to be monitored as healthy before DMP again
tries to schedule I/O requests on it.
The default value is 300 seconds.
A value of 0 prevents DMP from detecting
intermittently failing paths.
dmp_path_age
The default number of contiguous I/O blocks that are
sent along a DMP path to an array before switching
to the next available path. The value is expressed as
the integer exponent of a power of 2; for example 9
represents 512 blocks.
The default value of this parameter is set to 9. In this
case, 1024 blocks (1MB) of contiguous I/O are sent
over a DMP path before switching. For intelligent disk
arrays with internal data caches, better throughput
may be obtained by increasing the value of this
tunable. For example, for the HDS 9960 A/A array,
the optimal value is between 14 and 16 for an I/O
activity pattern that consists mostly of sequential
reads or writes.
This parameter only affects the behavior of the
balanced I/O policy. A value of 0 disables
multi-pathing for the policy unless the vxdmpadm
command is used to specify a different partition size
for an array.
See “Specifying the I/O policy” on page 180.
dmp_pathswitch_blks_shift
If DMP statistics gathering is enabled, set this tunable
to on (default) to have the DMP path restoration
thread probe idle LUNs. Set this tunable to off to
turn off this feature. (Idle LUNs are VM disks on which
no I/O requests are scheduled.) The value of this
tunable is only interpreted when DMP statistics
gathering is enabled. Turning off statistics gathering
also disables idle LUN probing.
The default value is on.
dmp_probe_idle_lun
Performance monitoring and tuning
Tuning VxVM
508